The present invention relates to an ink jet printer and, in particular, to an ink jet printer head.
Ink jet printer heads are known in the art as shown by U.S. Pat. No. 4,072,959 and include a plurality of nozzles and a piezoelectric transducer disposed behind the nozzles to apply pressure to ink, forcing ink through the nozzles. The piezoelectric transducer includes a vibrator placed almost rectangularly relative to the nozzle forming substrate and has a cantilever or center beam structure. The ink passages between the nozzles communicate with each other over a short distance.
Because the piezoelectric transducer includes a vibrator displaced almost rectangularly relative to the nozzle forming substrate and short nozzle ink passages, discharge efficiency and ink drop stability is high. Additionally, because the ink passages between nozzles communicate with each other over short distances, foreign matter such as bubbles, dust and the like mixed within the ink do not exert an influence during normal operation of the ink jet head. Moreover, because the vibrator is of a cantilever or center beam structure, electrical-mechanical transduction efficiency is high and the necessary vibrator displacement is obtainable at low voltages.
However, the prior art ink jet print head has been less than satisfactory. The stability of certain characteristics are inherently hard to obtain in the conventional ink jet head printers. The size of a gap formed between the vibrator and the nozzle substrate has an influence on characteristics such as ejection rate, ejection quantity and ejection answerability of ink drops. The gap size tolerance of the prior art ink jet print head is too limited to satisfy all these characteristic requirements. To increase ejection rate and ejection quantity of ink drops, it becomes necessary to maintain a gap between the nozzle forming substrate and the vibrator at an infinitesimal constant range to enhance ink pressure which exists near the nozzles. However, in such an infinitesimal gap, resistance and inertia is applied to the vibrator during displacement due to ink flow generated within the ink which exists in the gap between the vibrator and nozzle forming substrate. Accordingly, the periodic damping state changes to an impracticable setting for proper damping. For example, when subjected to excessive damping, a maximum ink ejection pressure value is minimized and the time required for reaching the maximum discharge pressure is lengthened relative to the situation in which the damping reaches a final displacement keeping a periodic damping having a long time constant. This results in a deterioration of energy efficiency. Additionally, a supply of ink necessary for restoring the nozzle meniscus for the next ink ejection is prevented by the gap between the vibrator and nozzle forming substrate so that the time for ink return within the gap becomes so long that answerability is deteriorated and ejection quantity fluctuation due to frequency becomes unavoidable.
Accordingly, it is desireable to provide an ink jet print head which overcomes the shortcomings of the prior art by controlling the gaps between the nozzle forming substrate and the transducer vibrator.